Low-cost and high-safety battery technologies are critical for both transportation and grid energy storage applications. Significant efforts have been made in the past years to move the energy storage beyond lithium-ion battery technology. Magnesium batteries are one promising technology because of the high volumetric capacity (3832 mAh/cm3 for Mg metal, in comparison 2062 mAh/cm3 for Li metal and 1136 mAh/cm3 for Na metal), improved safety (nondendritic and less chemically active compared to Na and Li metal), and potentially low cost given the natural abundance of Mg.
Traditional electrolytes for Mg batteries made by mixing conventional Mg salts (e.g., Mg(ClO4)2) and traditional solvents (e.g., propylene carbonate) do not typically support reversible plating/stripping of Mg. This is usually attributed to the formation of a solid electrolyte interphase (SEI) layer that does not conduct Mg2+ due to the two valence nature of Mg2+. Reversible Mg plating/stripping has been observed with some electrolyte compositions, almost all of them in-situ synthesized. However, most of these electrolytes contain highly volatile solvents, such as THF. Furthermore, none of the traditional electrolytes exhibit a sufficiently high cycling stability as measured by the coulombic efficiency—or the capacity fade. Therefore, a need exists for Mg energy storage devices and electrolytes for such devices that exhibit high cycling stability (i.e., little or no capacity fade for Mg plating/stripping).